<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title>计算器</title>
		<style>
			*{
				margin: 0px;
				padding:0px;
				box-sizing: border-box; /* 向内填充 */
			}
			
			.box{
				width: 300px;
				height: 400px;
				box-shadow: 0 0 10px rgba(0,0,0,0.3);
				margin:100px auto;
				padding: 20px;
				border-radius: 10px;
			}
			
			.box h3{
				text-align: center;
				margin-bottom: 10px;
			}
			
			/* >子元素选择器  css空格：后代 */
			.box>input{
				width: 100%;
				height: 30px;
				text-indent: 5px;
				outline: none;
			}
			
			.box .btns{
				display: flex;
				flex-wrap: wrap;
				justify-content: space-between;
				align-content: space-between;
				height: 250px;
				margin-top: 20px;
			}
			
			.box .btns input{
				width: 55px;
				height: 30px;
			}
		</style>
	</head>
	<body>
		<div class="box">
			<h3>计算器</h3>
			<input type="text" value="" />
			
			<div class="btns">
				<input type="button" id="" value="0" />
				<input type="button" id="" value="1" />
				<input type="button" id="" value="2" />
				<input type="button" id="" value="3" />
				<input type="button" id="" value="4" />
				<input type="button" id="" value="5" />
				<input type="button" id="" value="6" />
				<input type="button" id="" value="7" />
				<input type="button" id="" value="8" />
				<input type="button" id="" value="9" />
				<input type="button" id="" value="+" />
				<input type="button" id="" value="-" />
				<input type="button" id="" value="*" />
				<input type="button" id="" value="/" />
				<input type="button" id="" value="C" />
				<input type="button" id="" value="←" />
				<input type="button" id="" value="=" style="width: 100%;" />
			</div>
		</div>
	</body>
</html>
